Two more Vietnamese have contracted bird flu in the country’s north, a state-run newspaper reported on Monday, as more than 6,000 chickens were slaughtered in the southern Mekong Delta following a fresh outbreak.

The two were among five people admitted to a hospital in Hanoi with sore throat or bronchitis, the Saigon Giai Phong daily quoted hospital officials as saying.

The latest infections took the number of Vietnam’s bird flu patients since December to 64, 18 of whom have died.

The disease also killed 12 Thais and four Cambodians.

Health workers slaughtered and buried more than 6,000 chickens last week at a farm in the province of Ben Tre in the Mekong Delta after the birds were found to carry the H5 component of the bird flu virus, a state health official said.

The tests were conducted after the farm owner reported that more 3,000 of his chickens had died, Mai Van Hiep, director of the provincial animal health department told.

Ben Tre is one of the areas where the virus first emerged in late 2003 then spread to the northern region where the virus appears to develop rapidly during the winter.

“We do not exclude the possibility of an outbreak,” Hiep said by telephone from the province, 85 km (55 miles) southwest of Ho Chi Minh City.

Scientists fear avian flu, which is infectious in birds but does not spread easily among humans, could mutate into a form capable of generating a pandemic in which millions of people without immunity could die.

Last week, a Vietnamese doctor who treated bird flu patients tested positive for the virus.

But the Health Ministry insisted that there has so far been no evidence of human-to-human transmission of the virus.